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Unit 8.3 Class Amphibia. Tetrapods. Animals with 4 limbs. Amphibians Reptiles Birds Mammals Evolved from lobe finned fish in the Devonian period (middle of the Paleozoic). The first tetrapods were amphibians. Transition from Sea to Land. Coelacanth. Eusthenopteron. Panderichthys.
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Tetrapods • Animals with 4 limbs. • Amphibians • Reptiles • Birds • Mammals • Evolved from lobe finned fish in the Devonian period (middle of the Paleozoic). • The first tetrapods were amphibians.
Adaptations to live on land • Gills are usually lost by adulthood • Lungs function • Breathe through skin – Called cutaneous respiration • Secrete mucus • Prevent dehydration • Aids in respiration – Allows a medium through which oxygen can pass through skin to blood vessels.
More Adaptations to live on land • Skeleton • Fins evolve into limbs • Bony vertebral column supports body underneath it • Air is not as buoyant as water
Evolution of Circulation Fish Amphibian
Class Amphibia • Land and water • Reproduce in water • Skin with mucoid secretions • Respiration • No scales, feathers or hair • Heart with 3 chambers • 2 atria • 1 ventricle • One cervical vertebra – can turn neck only slightly • Exothermic – need a 4 chambered heart to be endothermic
Order Caudata • Salamanders comprise order. • A long tail is the defining characteristic of this order. • Salamanders have 4 legs. Usually, the front legs have 4 digits and the hind legs have 5 digits. • May be fully aquatic, amphibious, or fully terrestrial as adults
Paedomorphosis Paedomorphosis is the retention of juvenile characteristics in the adult form.
Family Plethodontidae • No lungs!! • Breathes through skin exclusively as an adult. • The larger of the two families of salamanders. • Lack aquatic larvae and hatch as miniature adults from eggs laid on land – must be very moist land!!
Family Salamandridae • Members have lungs. • True salamanders and newts. • Usually have rough skin (not as reliant on cutaneous respiration). • Usually brightly colored with contrasting bands. • Aquatic larval stage with external gills
Giant Salamander • The largest amphibians on the earth today. • Can reach sizes up to 1.8 meters (6 ft) in length. • Folds in their skin increase their surface area allowing for more oxygen absorption to occur.
Order Anura • Anura means “tail-less”. • Frogs and toads. • No tail in adult, but present in larval stage. • Long hind limbs, shortened body, and webbed feet characterize Anurans. • Considered to be the best jumpers of all vertebrates (up to 50 times their body length).
Toads vs. Frogs • Most toads arose due to convergent adaptations to drier climates, not separate lineages. • Skin is thicker to conserve water. • Lungs are better developed due to reduced cutaneous respiration.
Mating • Frogs often return to their pond of origin to breed. • Males call out to females with a sound unique to each species. • Mate by amplexus. The male mounts the female, stimulates her to release eggs by squeezing her pelvis, and then externally fertilizes the eggs.
Order Apoda • Caecilians are the only type of Apodan. • Defining feature is their lack of legs – resemble worms or snakes. • Skin glands produce mucous to assist in cutaneous respiration. • Live underground in tropical regions. • Least studied and understood amphibian.
Order Apoda • Caecilians have reduced eyes due to their subterranean lifestyle, but are not completely blind. • Many species undergo internal fertilization and have viviparous births. • Internal copulation may last 2 to 3 hours!
